1. Field of the Invention
The present invention is directed to a method and means for improving the maneuverability of a ship in ice-covered waters. More particularly, the invention is directed to a method and means for increasing the maneuverability of an ice-breaking cargo vessel which is navigating through ice-covered waters. The particular method includes positioning a means, which is in part comprised of a vertically oriented ice-crushing wall portion, into contact with ice on one side of the ship in order to create an imbalance of forces between that side of the ship and the other side, thereby forcing the ship toward said other side.
2. Description of the Prior Art
Discovery of oil fields and natural gas in the artic has led to an increased interest in the development of ice-breaking cargo vessels and/or tankers for use in transporting these resources to refineries and consumers at remotely situated markets. The cargo and/or tanker ships must operate efficiently during the transportation of their cargo. In order to operate efficiently, they must maintain a satisfactory speed with a relatively low fuel consumption. In order to meet these efficiency requirements, conventional ship designs have been developed. Such conventional designs have a low value of ship-ice resistance per unit cargo capacity. Such conventional designs are generally characterized by a relatively large length-to-beam ratio, fine bow forms and long parallel middle-body sections. Such hull designs allow the ship to perform efficiently during normal travel through non-ice-covered waters, and to perform well during straight travel through ice-covered waters. However, due to their relatively long parallel middle body sections, these conventional ships have poor maneuverability in ice-covered waters. The poor maneuverability of the conventional design has presented serious problems when attempting to turn these ships in order to change course in ice-covered waters to avoid objects, such as a major ice ridge or for maneuvering the ship into a docking facility. Accordingly, the poor maneuverability of such conventional designs within ice-covered waters deterimentally affects the safe operation and time required to effectively dock and position the vessel.
In order to avoid the above-mentioned safety hazards and attempt to minimize the transit time required to specifically maneuver the vessel, other ships have been designed to serve as the primary ice-breaking vessels. Such vessels escort the conventional cargo ships, clearing the path in front of the cargo ship. Such ice-breaking ships must have both a high maneuverability in the ice and cut a wide channel for the cargo vessel in which to follow. The necessary maneuverability, and ability to form a wide channel are made possible by providing such ice-breaking vessels with a stocky, rounded hull with a relatively low length-to-beam ratio, typically in the range of 4.0 to 5.5, such as disclosed in U.S. Pat. No. 857,766. The water plane-shape of this type of hull enables a certain degree of turning within the confines of the channel cut by the ship's beam. However, such a high beam-to-displacement ratio makes such a vessel configuration unsuitable as a cargo vessel. The high beam-to-displacement ratio results in a relatively high power requirement per unit cargo capacity which is moved. Furthermore, this high beam-to-displacement ratio results in an increased open water resistance per unit displacement. Therefore, such vessels do not travel efficiently through ice-covered or non-ice-covered waters.
Another design which has been developed in order to increase the maneuverability of a cargo ship in ice-covered waters includes a wide beam forward configuration, such as that disclosed within Canadian Pat. No. 947,482. The object of the wide beam forward design is to cause the ship's bow to cut a sufficiently wide channel through the ice to allow a relatively narrow middle body and stern to swing outward to either side during a turning maneuver. This concept has been embodied in a converted tanker SS Manhattan. While the wide beam forward design does provide a certain degree of improved turning capability in ice-covered waters, it suffers to some extent from the same effects as the stocky, rounded hull escort vessel discussed above. The wide beam forward configuration requires greater propulsion power per unit displacement in order to break through the ice than is required by an equivalent sized ship having a relatively high length-to-beam ratio. Therefore, although the wide beam forward configuration allows for greater maneuverability during turns in ice-covered waters, the design is inefficient for straight forward travel through ice-covered or non-ice-covered waters. The conventional fine hull shape with a long, parallel middle body section is a fuel efficient design. The fuel efficiency of this design is sacrificed to achieve improved maneuverability when the wide beam forward design is utilized.
Another prior art approach to the design of a more maneuverable ice-breaking cargo ship is the provision of a hull form characterized by a scooped-out section in the vicinity of the ice-breaking water line rearward from the point of maximum beam, such as disclosed in U.S. Pat. No. 3,727,571. The design of this hull is similar to that of the SS MANHATTAN-type hull discussed above, with the exception that the cargo capacity is increased by flaring the hull out to its maximum beam below the ice-breaking water line. While, to a lesser extent than the SS MANHATTAN-type hull design, the scooped-out hull design also loses cargo capacity and fuel efficiency at the expense of improved maneuverability within ice-covered waters.